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I am trying to do some measurements on VoIP. I am using OpenSIPS, RTPProxy, and SIPp for testing. Everything works fine as expected, but I only have a question regarding the delta time.

Below is a screenshot I got from Wireshark RTP streams' analysis.

enter image description here

Why do I have these spikes below the 20ms? I am using in a SIPp xml scenario, where 8kulaw has the following characteristics:

8kulaw.wav: RIFF (little-endian) data, WAVE audio, ITU G.711 mu-law, mono 8000 Hz

Much appreciated!

e19982456
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1 Answers1

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The "RTP Stream Analysis" from wireshark is giving you hints on the quality of the stream.

Your Max Delta value is 20.15 and occurs at packet 2008.

This will indicate the time between 2 packets which in your use-case are supposed to be spaced by exactly 20ms.

So the maximum difference is very short and should definitly not affect the quality of the stream. Usually, this is used on receiver (for incoming stream): on sender, there is usually no internal latency. This probably explains why you have so short "Max Delta".

The spikes you see are pretty big, but this is mostly because the scale is very short. Not because the stream is bad.

AymericM
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  • Thanks for the reply. It turned out that in SIPp's rtpstream.cpp, there is a sleep function sleeps until next iteration of playback loop. When I changed this to a small value (e.g., 1), the problem was solved. – e19982456 Feb 13 '20 at 19:02
  • Is there a reason why Wireshark does not show the mean delta? I am using tshark to export the RTP streams analysis. The output file contains mean/max jitter, max delta, but no mean delta. Do you have an idea how we can calculate mean delta from a pcap file? – e19982456 Feb 13 '20 at 19:13
  • I don't know about tshark. If you wish to add mean delta in wireshark, you will have to compute the value here: https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=ui/tap-rtp-analysis.c (also, I'm not sure the mean delta would be useful). The max delta is one of the most interesting value. – AymericM Feb 13 '20 at 23:35
  • Thanks AymericM. – e19982456 Feb 14 '20 at 16:55